Airspan ProST 4.9, Hardware Installation Manual

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605-0000-707 ProST 49 Installation User Guide-Rev C
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Fresnel Zones define the amount of clearance required from obstacles. These zones are
composed of concentric ellipsoid areas surrounding the straight-line path between two
antennas. Thus, the zone affects objects to the side of the path and those directly in the
path. The first Fresnel Zone is the surface containing every point for which the distance
from the transmitter to any reflection point on the surface point and then onto the receiver
is one-half wavelength longer than the direct signal path.
One method for clearing the Fresnel Zone is by increasing the antenna height.
The first Fresnel Zone radius is calculated by the following equation:
Where f is the frequency (in MHz) and d is the distance (in meters) between the ProST and
the base station.
For example, using the formula above, a link of 4 km at 4,900 MHz produces a first Fresnel
Zone radius clearance of about 61 meters. This implies that to ensure the ground does not
enter into the first Fresnel Zone, both radios (i.e. at base station and subscriber) must be
mounted at least 20 meters above ground level (or clutter level). Typically, at least 60%
clearance of the first Fresnel Zone is considered as LOS. Therefore, in the above example, a
height of at least 36 meters (i.e. 60% of 61 meters) above ground level is sufficient for
LOS.
Multipath Fading
Some of the transmitted signals may be reflected from a nearby building, by water under
the signal path, or from any other reflectors. This reflected Some of the transmitted signals
may be reflected from a nearby building, by water under the signal path, or from any other
reflectors. This reflected ("bounced") signal can then be received by the radio receiving the
signal and superimposed on the main received signal, thereby degrading the signal
strength.
To avoid multipath fading from nearby buildings etc., Airspan recommends installing the
ProST at the rear end of buildings instead of at the front. When you install at the rear end
of the building, the front-end of the building blocks incoming signals from multipath
reflections.
Radio Antenna Alignment
Once the ProST is installed and aimed in the general direction of the base station, it is
recommended to measure the received signal strength (RSS) to determine the signal
strength received from the base station, and to precisely align the ProST for maximum
signal strength. You need to orientate (up/down, left/right) the ProST until the maximum
RSS levels are achieved, and then secure the ProST. (For viewing the received signal
strength, see "ProST Web-Based Management".